1. Field of the Invention
This invention relates generally to apparatus for mounting an electron gun assembly within the glass neck of a cathode ray tube envelope, and more particularly is directed to improvements in the structure by which the electron gun assembly is supported during the fusing or welding of the glass neck of the cathode ray tube envelope to the glass stem of the electron gun assembly.
2. Description of the Prior Art
In the manufacturing of cathode ray tubes, for example, for color television receivers, after a phosphor screen has been formed on the inner surface of a glass face plate, an aperture grill is attached to the face plate which is then secured, at its periphery, to the large end of a funnel-shaped envelope having a relatively small diameter neck. Then, an electron gun assembly is inserted into the glass neck of the envelope and secured or mounted therein by fusing or welding together a glass stem of the gun assembly and the neck of the envelope. After the electron gun assembly is thus mounted in the envelope, gas is evacuated from the latter by way of an exhaust tubulation which extends centrally from the stem of the gun assembly. Then the exhaust tubulation is sealed or tipped-off for maintaining the evacuated condition of the envelope.
During the mounting of the electron gun assembly in the neck of the cathode ray tube envelope, the electron gun assembly is supported by an upright support tube having a central bore extending therethrough for receiving the exhaust tubulation of the electron gun assembly with the glass stem of the latter arranged above the upper end of the support tube. The metallic leads of the electron gun assembly which extend through the stem in a circle about the tubulation for electrical connections to gun elements in the envelope are accommodated in auxiliary bores opening at the upper end surface of the support tube and being arranged in a circle about the central bore. While the cathode ray tube envelope is suitably supported with its glass neck directed downwardly, the electron gun assembly carried by the support shaft is inserted upwardly into the glass neck by means of a vertically movable spindle in which the support shaft is disposed. When the electron gun assembly is suitably positioned in the neck, the glass neck is gradually heated in the vicinity of the electron gun stem by one or more burners and, when the neck and stem are sufficiently heated they are fused or welded to each other. After such welding, the portion of the glass neck below the stem is severed and drops away, whereupon the neck and stem are cooled gradually to avoid cracking thereof.
For the severing of the lower end portion of the neck below the glass stem to which the neck is fused, nitrogen gas under pressure is supplied through the spindle and then through the central bore of the support tube to exit from the latter immediately under the stem through the upper end of the central bore and also through the auxiliary bores which loosely receive the metallic leads so as to exert outwardly directed pressure against the glass neck immediately below the fusing or welding thereof to the stem.
However, in the foregoing arrangement according to the prior art for supplying the nitrogen gas under pressure by way of the central bore of the support tube which also receives the exhaust tubulation of the electron gun assembly, the nitrogen gas under pressure and any dust particles, usually of glass, carried thereby is also delivered to the interior of the cathode ray tube envelope. Such dust particles within the cathode ray tube envelope give rise to problems. Thus, for example, if the dust particles adhere to the phosphor screen or are caught between the elements of the aperture grill, black dots will appear on the screen at locations corresponding to the dust particles. Further, due to the high voltage applied to the interior of the cathode ray tube envelope, dust particles therein cause a discharge which damages the cathode of the electron gun. Similarly, if the dust admitted to the interior of the envelope adheres to the cathode of the electron gun, this also causes discharging and consequent damage. If the dust is caught between grids of the gun, leaking or sparking in the electron gun can result.